Devices for use in free piston machines to indicate when the maximum pressure in the power unit cylinders of such machines exceeds a predetermined value



Oct. 4, 1960 R. HUBER 2,954,761

DEVICES, FOR USE IN FREE PISTON MACHINES, TO INDICATE WHEN THE MAXIMUM PRESSURE IN THE POWER UNIT CYLINDERS OF SUCH MACHINES EXCEEDS A PREDETERMINED VALUE Filed Dec. 9, 1958 DEVICES FOR USE IN FREE PISTON MACHINES TO INDICATE WHEN THE MAXllVIUM PRES- SURE. IN THE POWER UNIT CYLINDERS OF "SUCH MACHINES EXCEEDS A PREDETER MINED VALUE Robert. Huber, Bellevue, France, assignor to So'ciete dEtudes et de Participations Earl, Gaz, Electricite Energie S.A., Geneva, Switzerland, a Swiss society of the cylinder and piston type and the piston of which is rigid with the'power unit piston and in line therewith,

the term free piston meaning that, in at least one direction of its reciprocating movement, the piston assembly stroke is not mechanically limited (so that the present invention is concerned both with machines having Wholly free pistons and machines having semi-free pistons).

Such machines may be either of the auto-generator type or of the motor compressor type.

The object'of my invention is to provide, in such a machine, a device for indicating when the maximum pressure in the power unit cylinder exceeds a given value.

It is known to provide the cylinder of a diesel engine, for safety purposes, with maximum pressure indicators or safety valves which open when the pressure in the engine cylinder exceeds a limit value.

It-would be desirable to provide the power cylinders of free piston machines with safety devices of this kind.

However it is not possible to provide a free piston machine power cylinder with a safety valve opening when the maximum pressure in said cylinder exceeds a predetermined value because, in machines of this kind, the strokes of the pistons in their cylinders are not limited, so that, under the effect of-an excessive maximum pressure, such valves might allow too great an amount of gas under pressure to escape from the cylinder. in this case,the pisto'ns might strike very violently the cylinder head or two pistons workingin opposition might strike each other in a violent fashion, thus causing injury of the machine.

On the other hand it is extremely diflicult, not to say impossible, to fit pressure gauges or analogous pressure indicators on the power cylinders of free piston machines, both because the pressures and temperatures in such cylinders are very high and because the place available for mounting them is very small.

The object of the present invention is to provide a de vice which, despite the above stated difficulties, gives a warning when the maximum pressure in the power cylinders exceeds a given value, which will be hereinafter called reference value.

The invention is based upon the fact that the acceleration of the piston of a free piston machine is substantially proportional, at the beginning of its power stroke, to the pressure in the power cylinder where said pistonis lo cated.

The invention consistsin the combination of warning, or signalproducing, means with accelerometric means operatively connected with the pistons and capable, when they detect anacceleration of said pistons equal to or exceeding a given value, of operating said signal producing means. 7

Preferred embodiments of the present invention will 2,954,761 Patented Oct. 4, 1960 2 and 3, corresponding to a third embodiment of the invention.

Fig. 1 shows a first embodiment of the invention for use in connection with an auto-generator. This autogenerator includes two cylinders coaxially in line with each other, the. firstcylinder 1 being a power cylinder whereas the second cylinder 2 constitutes, in the portion 2a thereof turned toward cylinder 1, a compressor cylinder and, in the opposed portion 2b, an energy accumulator for returning the pistons in the upward direction. A double piston cooperates with these two cylinders, the portion 3 of this double piston constituting a power piston which cooperates with power cylinder 1, whereas the portion 4 of the double piston cooperates with cylinder 2 and constitutes a compressor piston, its annular face turned toward the power piston 3 serving to suck in and to compress air in the portion 2aof cylinder 2, whereas its opposed face cooperates with 'the air cushion imprisoned in the portion 2b of cylinder 2.

Power cylinder 1 is provided with an injector 5 and with intake ports 6 and exhaust ports 7, the opening and closing of these ports being performed by piston 3.

The chamber 2a of cylinder 2 is provided with one or several air inlet check-valves 8 and with one or several delivery check-valves 9 past which compressed air is transferred into an air reservoir 10 constituted by a casing which surrounds power cylinder 1.

Air is therefore suckedin past check-valve 8 when piston 34- is moving outwardly under the effect of the combstion of fuel in cylinder 1 and it is compressed and delivered into reservoir 10 when piston 3-4 is moving in the opposed direction under the action of the energy accumulated in compartment 2b during the preceding stroke of the piston.

The air compressed in reservoir 16 serves to scavenge power cylinder l'when ports 6 are opened by piston 3 and to feed said power cylinder with fresh air.

The discharge ports 7 of the power cylinder 1 are connected through a conduit 11 with a manifold 12 for any suitable use (for instance in a gas turbine), the gases delivered by each of the auto-generators into said main conduit 12 consisting of a mixture of compressed air (scavenging air introduced into cylinder 1) and of combustion gas incompletely expandedin the power cylinder 1, this mixture escaping through ports 7 during the period for which said ports are uncovered by the corresponding piston 3.

The injector 5 is fed with fuel through a conduit 13 leading from an injection pump which includes a cylinder 14 in which a piston is moved through a push-piece 15 driven, from the compressor piston 4, by mechanical means including a rod 16, a link 17 and a lever 18.

For the sake of simplicity, the drawing shows an autogenerator having only one double piston 3-4 but, in

actual practice, auto-generators generally include two rigid with piston 4, and a second element 20. adapted to cooperate with the first one and including a stem 21 slidthe machine, to rod 19.

wound around stem 21 and interposed between element 20 and a portion of support23 urging element 20 so as normally to apply it against element 19.

Parts 19, 20, 21 and 23 are made of a. conductor material, but an insulating sleeve 25, which constitutes the mechanical connection between rod 19 and support 23, forms an electric separation between said parts 19 and 23. A resilient plate 26, which forms a sliding contact with conductor support 23 and which-is insulated (by an insulating part 46) from the mass of the machine, is connected, through a conductor 27, to one of the terminals of a relay 28. The other terminal of said relay 28 is connected, through a conductor 29 and the metallic mass of A source of electric current 30 tion suificient to cause mass 33 to pivot about said axis 34 so that contacts 39 and 40 are separated from each other, which cuts ofi the flow of current to relay 28, and

a this relay operates the signal producing device 31.

is inserted in the circuit of relay 28, so as to cause a signal a to be transmitted by a device 31 (for instance by means of a loud-speaker supplying a sound signal) when the energizing current flowing through the above mentioned circuit is cut oif.

The operation of the device of Fig. 1 is as follows. As long as the acceleration of piston 3-4, and consequently of rod 19, does not exceed a given value, corresponding to the above designated reference pressure, element 20, under the efiect of spring 24, moves together with rod 19, which causes circuit 19, 20, 21, 23, 26, 27, 28, 29, 30 to be closed. I

'On the contrary, as soon as the acceleration of piston 3-4 in the outward direction exceeds said given value determined by the strength of spring 24, element 20 cannot follow rod 19, and the above mentioned circuit is cut off between 19 and 2t Relay 28 then operates the warning, or signal producing, device 31 so that a signal is delivered which indicates that a maximum pressure higher than the reference pressure is reached in power cylinder 1.

Fig. 1 further shows an indicator lever 32, mechanically connected with the free piston 3-4 and indicating on a graduation 53 the positions of piston 3-4, and in particular the innerand outer dead center positions. This indicator lever 32 may for instance be mounted on the lever 18 which controls the push-piece of the injection pump. It might also be mounted on the axis of oscillation of the means which are often provided in such machines for synchronizing the movements of two opposed double pistons.

According to a second embodiment of my invention, the cooperating parts of the accelerometric device which starts the signal producing device may be mounted on lever 32.

For instance, in the construction illustrated by Figs. 2 and 3, lever 32 carries a mass 33 pivoted thereto at 34 and having its center of gravity at 35. This part 33 includes an arm 36 subjected to the action of a spring 2311 (bearing upon an abutment 38 carried by lever 32) so that its lower contact 39 is urged against a contact 40 carried by lever 32. In this construction, relay 28 which operates the signal producing device 31 is connected, on the one hand with lever 32 by conductor 29, and on the other hand through conductor 27 to a resilient contact 26a bearing against conductor part 24a connected by a conductor 45 with contact 49. Insulating pieces 46a and 47 serve to form an electric separation between conductor 45 and the support 24a of lever 32.

The operation of the device of Figs. 2 and 3 is as follows.

As long as the acceleration of the movement of rotation of lever 32 in the direction corresponding to the outward displacement of piston 3-4 does not exceed a given value corresponding to the reference pressure, spring 23a applies contact 39 against contact 40, so that the feed circuit of relay 28 is closed. On the contrary, when, at the beginning of the power stroke of piston 3-4, the acceleration of this piston exceeds a value corresponding to the reference pressure, lever 32, in the course of its rotation in the direction of arrow F, drives pivot 34 with an accelera- If the strength of spring 23 or 23a is modified, it is possible to modify the value of the maximum pressure in the power cylinder for which the device gives a warning. It is particularly advantageous to be able to vary the strength of said spring while the machine is working. For instance, in the embodiment of Figs. 4 and 5, the contact 39 carried by arm 36 cooperates with a movable contact 40a carried by a lever 41 pivotable about an axis 42, the free end 43 of this lever being thus movable in front of a graduation 44 (Fig. 4).

When lever 41 is pivoted about its axis 42, the strength of spring 23a is varied, which has for its efiect to cause contacts 39 and 40a to be moved away from each other for different accelerations of lever 32. Of course, the graduation 44 may indicate directly the maximum pressures (in cylinder 1) corresponding to the accelerations for which contacts 39 and 40a are moved away from each other.

' The remainder of the arrangement shown by Figs. 4 and 5 is similar to that of Figs. 2 and 3 and the same elements are designated by the same reference numerals.

The opertaion of the device of Figs. 4 and 5 is as follows.

If the end 43 of lever 41 is first placed upon a graduation 44 corresponding to a relatively high maximum pressure in cylinder 1, it is probable that no signal will be delivered by device 32, which means that contacts 39 and 4011 are never moved away from each other and that the pressure in cylinder 1 does not exceed the pressure indicated by the graduation 44 opposite which the end 43 of the lever has been positioned. Said lever 41 is then gradually moved so that its end 43 comes opposite graduations corresponding to lower and lower pressures, until a signal is obtained from device 32, this signal warning the operator that the pressure indicated by the free end 43 of the lever is reached in power cylinder 1.

It is thus possible to effect measurements of the maximum pressure existing in the power cylinder of a free piston machine.

It should be well understood that the invention applies not only to the case where it is desired to detect an abnormal'increase of the acceleration of a free piston moving in the outward direction, but also that where it is desired to detect a sudden deceleration (under the effect of too high a pressure in the power cylinder) of said piston moving in the inward direction.

The device above described is capable of working at high values of the pressures and temperatures existing in the power cylinder. It may be disposed at any place where suflicient room is available. 7

Its operation is sufficiently correct and accurate to ensure an eflicient safety.

Of course, the construction above indicated has been given merely by way of example and modifications might be brought thereto. In particular, the existence of an acceleration corresponding to the reference pressure in the power cylinder might produce a movement of the two above mentioned elements toward each other instead of away from each other, as above described, in order to close an electric circuit instead of opening it.

Of course also, the control of the signal producing device might be effected through hydraulic, pneumatic or electronic means, instead of being obtained through electric means as above described.

In a general manner, while I have, in the above description, disclosed what I deem to'be practical and efficient embodiments of my invention, it should be weli understood that I do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as comprehended within the scope of the accompanying claims.

What I claim is:

1. In a free piston machine of the type described including 'an internal combustion power unit and an air compressor unit, each of said units including a cylinder and a piston fitting slidably in said cylinder, the two cylinders being in line and in fixed position with respect to each other and the two pistons being rigid with respect to each other, a device for indicating when the maximum pressure in said power unit cylinder exceeds a given value, said device comprising, in combination, means capable, when energized, of delivering a signal, and accelerometirc means operatively connected with said pistons for energizing said signal producing means when the acceleration of said pistons 'at the beginning of the power strokes of said combustion power unit exceeds a predetermined value.

2. In a free piston machine of the type described including an internal combustion power unit and an air compressor unit, each of said units including a cylinder and a piston fitting slidably in said cylinder, the two cylinders being in line and in fixed position with respect to each other and the two pistons being rigid with respect to each other, a device for indicating when the maximum pressure in said power unit cylinder exceeds a given value, said device comprising, in combination, means capable, when energized, of delivering a signal, a part movably guided with respect to said cylinders, positive means for operatively connecting said part with respect to said pistons, another part movably guided with respect to said cylinders with a movement corresponding to that of said first mentioned part, resilient means interposed between said two parts for yieldingly keeping said second mentioned part in fixed position with respect to said first mentioned part, and means operative by relative movement of said second mentioned part with respect to the first mentioned one for energizing said signal producing means in response to such a relative movement.

3. A device according to claim 2 in which said first mentioned part is rigidly carried by said pistons and said second mentioned part is slidable with respect to said pistons in the direction of their movement.

4. A device according to claim 2 in which said first mentioned part is pivoted with respect to said cylinders about a transverse axis perpendicular to the axis of said cylinders, and said second mentioned part is pivoted to said first mentioned part about an axis parallel to said transverse axis.

5. A a device according to claim 1 in which said resilient means is adjustable during operation of said machine.

References Cited in the file of this patent UNITED STATES PATENTS 

